This invention relates to vehicle shock absorbers typically mounted between the wheels and frame of an automobile, truck, motorcycle, etc. The invention relates to a shock absorber with damping characteristics that change depending on the acceleration of parts of the shock absorber.
This application is related to U.S. patent application Ser. No. 07/798,036, filed Nov. 20, 1991.
Hydraulic shock absorbers are universally employed in automotive vehicles. Each wheel of the vehicle is coupled to the frame by a spring so that bumps or dips in the road are not transmitted directly to the passengers or vehicle lead. A spring alone, however, would still give a rough ride. Shock absorbers are therefore mounted in parallel with the springs to damp the accelerations applied to the frame from the wheel. There is a long history of shock absorber development to obtain desired characteristics of passenger ride, comfort, handling for steering, road traction and the like.
Most shock absorbers are designed to have a certain operating characteristic or load-velocity curve which is a compromise of the characteristics desired for a variety of road conditions. The characteristics suitable for driving on relatively smooth road may, however, be inappropriate where the vehicle wheels may encounter short range bumps or dips. Such conditions are not limited to vehicles like those used on off-road terrain, but also include ordinary passenger and freight vehicles which may unexpectedly encounter chuck holes, speed bumps or foreign objects on the roadway.
Efforts have therefore been made to provide shock absorbers with variable characteristics in response to varying road conditions. Attempts to have been made to have computer controlled shock absorbers employing sensors, solid state computers which are preprogrammed, and electrically operated valves controlled by the computer. As with any computer, its output is no better than its input and even though the speed of response is indeed amazing, the overall system response, including that of the mechanical valves, determines the actual speed of adjustment.
A vehicle traveling at about 100 km/h advances over the ground approximately 16 centimeters in five milliseconds. A computer controlled system which has an overall response time in that range cannot provide effective compensation for surface conditions based on any remote sensing of either present or anticipated road conditions. The acceleration of the wheel upon hitting a bump or dip may be over before the system can adequately respond. Furthermore, by directing optical or other sensors ahead of the vehicle, the sensors incur problems of dust, rain or other conditions which may mask the true road condition and prevent effective computer controlled compensation.
Another approach is to employ acceleration responsive valves which require no computer or manual adjustment. A number of acceleration responsive shock absorbers have been proposed which internally respond to accelerations for providing automatic adjustment of orifices in the shock absorbers. Many of these systems are limited since they provide no reduction in rebound resistance or resistance to extension of the shock absorber in the presence of terrain defects, particularly, sharp dips.
There are two principal types of shock absorbers employed on automotive vehicles. One of them comprises a single tube or cylinder with a piston in the cylinder. A variety of valves and orifices are used for controlling flow of hydraulic shock absorber fluid from one end of the cylinder to the other end through the piston. A variety of acceleration sensitive adjustments have been proposed for this type of shock absorber.
The other principal type of shock absorber has twin tubes. In this type of shock absorber there are concentric tubes with a piston in the inner tube. The annulus between the inner and outer tubes serves as a reservoir for hydraulic fluid and may serve as a pressure accumulator. Sometimes such shock absorbers may be connected to an external pressure accumulator. No efforts are known with respect to providing an acceleration sensitive twin tube shock absorber.
It is also desirable that such an acceleration sensitive shock absorber have essentially instantaneous changes in characteristics when subjected to acceleration in either compression or extension. It is also desirable that the shock absorber include means for assuring a change of characteristics near the end of the stroke of the shock absorber so that the piston does not "bottom" against a hard metal end.